To brute force every 2-character alphanumeric passphrase with no salt, you would have to run the scrypt function 38.4 billion times (each with 2^16 iterations). Adding an email address as your salt could make it impractical to brute force.

In my short test, the time-consuming part (at least in the javascript implementation) seems to be the iteration of the PIN. Now by your construction one doesn't have to brute-force this part, since computing this part for PIN=9999999 will also compute this part for all smaller PINs.

Wouldn't it be better to just append the PIN to the salt and instead increase the number of scrypt iterations until the code has roughly the same run-time as before with a seven digit PIN?

I would be already happy when a website would offer the signature verification tool. It was a very quick and easy way to copy paste a signature and check it there. Wallets and coinig need 3 times copy past, including carefully chosing the signs to copy.

I would like to have this tool. I don't need anything other that was on brainwallet.org. I guess bringing that tool online would be no risk at the moment right? So hopefully someone does.